powerpc/pasemi: Turn on devtmpfs in defconfig

At least some distros expect it these days; turn it on. Also, random
churn from doing a savedefconfig for the first time in a year or so.

Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>